A chemical model that predicts three-dimensional molecular geometries based on electron pair repulsions.

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) Theory is a fundamental model in chemical bonding that explains and predicts the three-dimensional shapes of molecules based on the electrostatic repulsion between electron pairs.

Core Principles

Electron pairs in a molecule's valence shell repel each other and arrange themselves to minimize these repulsions
Both bonding and lone pairs contribute to molecular geometry
The arrangement of electron pairs determines the final molecular shape

Electron Domain Geometries

The basic geometries predicted by VSEPR theory include:

Two electron domains: Linear (180°)
Three electron domains: Trigonal planar (120°)
Four electron domains: tetrahedral structure (109.5°)
Five electron domains: Trigonal bipyramidal
Six electron domains: Octahedral

Factors Affecting Molecular Shape

Lone Pair Effects

Lone pairs occupy more space than bonding pairs, leading to:

Increased repulsion
Decreased bond angles
Distorted geometries

Electronegativity

Electronegativity differences between atoms can cause:

Bond polarization
Slight geometric distortions
Modified electron distribution

Applications and Limitations

VSEPR theory successfully predicts:

Basic molecular geometries
Bond angles (approximately)
Relative spatial arrangements

However, it has limitations in:

Transition metal complexes
Molecular orbital theory considerations
Electronic effects beyond simple repulsion

Historical Development

Developed by Ronald Gillespie and Ronald Nyholm in 1957, VSEPR theory built upon:

Lewis structures
Earlier bonding theories
Experimental observations of molecular shapes

Modern Usage

VSEPR theory remains crucial in:

Introductory chemistry education
Quick prediction of molecular shapes
Understanding basic molecular polarity
Foundation for more advanced structural theories

Related Concepts

The theory connects strongly to:

This fundamental theory provides a straightforward approach to understanding molecular shapes, though more sophisticated models are needed for complete accuracy in complex systems.